1. Field of the Invention
The present invention relates to an optical scanning device mounted on an image forming apparatus.
2. Description of the Related Art
An optical scanning device used in an image forming apparatus employing an electrophotographic method includes optical components such as a light source, a rotating polygon mirror, an fθ lens, and a reflection mirror. A light beam is emitted from the light source according to an image signal, and then deflected by the rotating polygon mirror that is driven to rotate. The deflected light beam is reflected by the optical component such as the reflection mirror, and then a photosensitive member including a photosensitive layer is irradiated with this light beam. As a result, an electrostatic latent image based on the image signal is formed on the photosensitive member.
This optical scanning device includes a motor used for driving the rotating polygon mirror to rotate and an integrated circuit (IC) used for controlling the motor. In this optical scanning device, thermal expansion of an optical box occurs due to the heat produced by the motor and the IC, which leads to deformation of the optical box. This deformation results in a change in a relative position of the optical component contained in the optical box. As a result, the optical scanning device cannot form an electrostatic latent image at a desired position on the photosensitive member, which reduces quality of an output image.
There is known a technique that suppresses a change in a relative position of an optical component caused by heat from driving units, by providing slits around an installation region where the driving units are disposed (see, for example, Japanese Patent Application Laid-Open No. 2011-170027). The driving units include a motor and an IC that are used for driving a rotating polygon mirror to rotate. In other words, when thermal expansion of an optical box occurs due to the heat of the driving units, the slits provided in the optical box absorb deformation of the optical box.
Here, when a rotation speed of the rotating polygon mirror is increased to increase a printing speed of an image forming apparatus, the amount of heat generated from the driving units grows. This leads to an increase in deformation amount of the optical box. Therefore, it is necessary to increase the width of each of the slits provided in the optical box, to extend the length of each of the slits, or to increase the number of the slits. However, when the width of the slit, the length of the slit, or the number of the slits is increased, rigidity of the optical box considerably decreases, which is a problem.